Callback function for ping results.
This function is called for every echo packet sent.
If the deadline is exceeded, it is not called for the remaining packets.
If the echo response has been received, the error value will be null,
otherwise it contains the error.
Callback function for ping results. This function is called for every echo packet sent. If the deadline is exceeded, it is not called for the remaining packets. If the echo response has been received, the error value will be null, otherwise it contains the error.